Transverse fan with randomly varying I-shaped tongue

ABSTRACT

A vortex wall (14) and impeller (30) assembly for a transverse or cross flow fan (10). The wall is intended to reduce blade rate tonal noise and is formed in a number of segments (15). The segments have noses with J shaped cross sections and are arranged so that the J tail (16) of one segment points in the opposite direction from the J tail of an adjacent segment. The spanwise widths (W), segment-to-impeller clearances (c) and setting angles (θ) vary randomly, within specified limits, among the segments.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of air moving apparatussuch as fans and blowers. More specifically, the invention relates to afan of the transverse type. Transverse fans are also known as cross-flowor tangential fans.

The operating characteristics and physical configuration of transversefans make them particularly suitable for use in a variety of air movingapplications. Their use is widespread in air conditioning andventilation apparatus. Because such apparatus almost always operates inor near occupied areas, a significant design and manufacturing objectiveis quiet operation.

FIG. 1 shows schematically the general arrangement and air flow path ina typical transverse fan installation. FIG. 2 shows schematically themain features of a typical transverse fan installation. FIG. 3 shows themain features of a typical transverse fan impeller. Fan assembly 10comprises enclosure 11 in which is located impeller 30. Impeller 30 isgenerally cylindrical and has a plurality of blades 32 disposed axiallyalong its outer surface. Impeller 30 comprises several modules 32, eachdefined by an adjacent pair of partition disks 34 or by one end disk 33and one partition disk 34. Between each adjacent pair of diskslongitudinally extend a plurality of blades 31. Each blade is attachedat one of its longitudinal ends to one disk and at the other end to theother disk of the pair. A given impeller may comprise multiple modulesas depicted in FIG. 3 or but a single module, where the blades attach ateither end to an end disk. The choice of a single or multiple moduleconfiguration depends upon such factors as fan size, constructionmaterial strength and weight and the like. As impeller 30 rotates, itcauses air to flow into enclosure 11 into inlet plenum 21, throughimpeller 30 and out of enclosure 11 through outlet plenum 22. Rear orguide wall 16 and vortex wall 14 each form parts of both inlet andoutlet plena 21 and 22. Vortex wall 14 has nose 15 which is that portionof wall 14 closest to impeller 30. The general principles of operationof a transverse fan need not be further elaborated upon except asnecessary to an understanding of the present invention.

When a transverse fan is operating, it generates a certain amount ofnoise. One significant component of the total noise output of the fan isa tone having a frequency related to the rotational speed of the fanmultiplied by the number of fan blades (the blade rate tone). Thepassage of the blades past the vortex wall produces this blade ratetone. Tonal noise is in general more irritating to a listener than broadband noise of the same intensity. The blade rate tone produced by thetypical prior art transverse fan has limited the use of such fans inapplications where quiet operation is required.

Manufacturing a transverse fan having randomly or nonuniformly spacedparts to reduce blade tonal noise is known in the art, see e.g. U.S.Pat. No. 4,538,963 (issued 3 Sep. 1985 to Sugio et al.) and U.S. Pat.No. 5,266,007 (issued 30 Nov. 1993, one of the inventors of which isalso an inventor of the present invention and which is assigned to thesame assignee as the present invention.

It is the interaction between air flow associated with the fan bladesand the vortex wall that produces the blade rate tone in a transversefan. Therefore one can reduce the blade rate tone by any means thatreduces the regularity of the interaction between the blades and thevortex wall.

SUMMARY OF THE INVENTION

The present invention is a vortex wall and impeller assembly for atransverse fan installation. The passage of the blades of the fanimpeller past the vortex wall cause pressure pulses that are a source oftonal noise. The wall and impeller of the present invention causesirregularity in the amplitude and phase of the pressure pulses and thuscan reduce the blade rate tonal noise.

The vortex wall is divided into spanwise segments. Each segment has anose that is J-shaped in cross section. The segments are configured sothe tails of the Js in adjacent segments extend in opposite directions.The segments are arranged so that wall-to-impeller clearances varyrandomly, within limits, among the segments. The setting angles of thesegments also vary randomly within limits.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings form a part of the specification. Throughoutthe drawings, like reference numbers identify like elements.

FIG. 1 is a general view, partially broken away, of a typical transversefan installation.

FIG. 2 is a schematic diagram of the principal parts of and air flowpath through a typical transverse fan.

FIG. 3 is a pictorial view of a typical transverse fan impeller.

FIG. 4 is a pictorial view of the nose of the vortex wall of the presentinvention.

FIG. 5 is a cross sectioned view of the nose of the vortex wall of thepresent invention.

FIG. 6 is a another cross sectioned view of the nose of the vortex wallof the present invention in relationship to an impeller.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The general information presented in the Background section above on theconfiguration and operation of a transverse fan apply to a fan having avortex wall configured according to the teaching of the presentinvention.

FIG. 4 shows a portion of the nose of vortex wall 14. It is the nose ofwall 14 that is closest to the impeller in a fan installation. Over thespan S of wall 14, it is divided into at least two segments, typified bysegment 15. The nose of segment 15, as shown in FIG. 5, has a J-shapedcross section and J-tail 16. The segments are configured to form wall 14so that the tails of the Js of adjacent segments point in oppositedirections. The spanwise width of segment 15 is W.

FIG. 6 shows an elevation view of vortex wall 14 together with itsassociated impeller 30. Impeller 30 rotates about center of rotationC_(R) and has maximum swept diameter D. The distance between a segmentand impeller 30 at its maximum swept diameter is clearance c. c₁, c₂ andc₃ are the clearances for the three segments visible in FIG. 6. Eachsegment has a discrete vortex wall setting angle θ. The vortex wallsetting angle is the angle between an arbitrary radial line from centerof rotation C_(R) and a radial line from center of rotation C_(R) andthe point on the segment nose where clearance c for that segment isleast. θ₁, θ₂ and θ₃ are the setting angles for the three segmentsvisible in FIG. 6.

For best noise reduction performance, the spanwise width of the segmentsin a particular vortex wall should vary, within limits, randomly. Theoptimum spanwise width and number of segments in a wall invention is afunction of several considerations including the overall length of theimpeller with which the vortex wall will be used, the number of modulesin that impeller and the configuration of the blades in the impeller. Inthe atypical case of a very short impeller, where the ratio of theimpeller length to impeller diameter is less than one, then the spanwisewidth of the segments may be on the order of 0.4 times the span and avortex wall having just two segments may provide the best noisereduction. In the more general case, where the ratio of impeller lengthto impeller diameter is greater than three, the spanwise width of thesegments may be on the order of 0.2 times the span. There is a lowerlimit on the minimum width of an individual segment and the number ofsegments in a given wall. If the segments are too narrow, then theability of the wall to reduce noise may be impaired. We believe thatoptimum noise reduction performance is achieved when no segment has awidth that is less than 0.01 times the overall span of the wall and nosegment has a width that is more than 0.5 times that overall span, or0.01 S<W<0.5 S. If the impeller is separated into modules, the number ofsegments in the vortex wall should be about 25 to 50 percent more thanthe number of modules. Further, the placement of the segments should beso that a single segment bridges across two adjacent modules.

The air moving performance of a transverse fan improves as the clearancebetween the impeller and the nose of the vortex wall decreases. Ingeneral, however, the noise produced by the fan also increases as thevortex wall-to-impeller clearance decreases. A good compromise betweenis to maintain nose-to-impeller clearance within the range of 0.04 to0.12 times the swept diameter of impeller. To promote flow and pressureconditions in the fan that will minimize blade rate noise, we believethat the nose-to impeller clearance of the segments in the vortex wallshould vary among the segments randomly within that range of 0.04D<c<0.12 D.

Varying setting angles among the segments has beneficial effects onnoise reduction but excessively wide variations could result indegradation of overall fan performance. The setting angles should varyrandomly among the segments within the bounds that no segment has asetting angle that is greater than 30 degrees different from the settingangle of any other segment or, Δθ_(max) =30°.

As a an example of a suitable configuration for the vortex wall andimpeller configuration for a fan of a typical size, we believe that foran impeller of approximately 40 cm in length and having seven modules,the overall span of the associated vortex wall would also beapproximately 40 cm long, within that span the wall should be dividedinto 11 or 12 segments, the setting angles of the segments should varyrandomly with no segment having a setting angle that is greater than tendegrees different from the setting angle of any other segment, and theratio of the clearance to the maximum swept diameter of the impellershould vary randomly between 0.06 band 0.08.

We claim:
 1. A vortex wall (14) and impeller (30) assembly for atransverse fan (10), said impeller having a maximum swept diameter (D)and said wall having a span (S), comprising at least two segments (15),each of said segments havinga nose having a J-shaped cross section witha J tail (16), a spanwise width (W), a nose-to-impeller clearance (c)and a setting angle (θ);and said segments being arranged to form saidwall so that a J tail of a given segment extends in the oppositedirection from the direction in which the J tail of an adjacent segmentextends, said spanwise widths vary randomly among the segments withinthe bounds that no segment has a spanwise width that is less than 0.01times nor more than 0.5 times said span, said nose-to-impellerclearances vary randomly among the segments within the bounds that nosegment has a clearance that is less than 0.04 times nor more than 0.12times said maximum swept diameter, and said setting angles vary randomlyamong the total number of segments within the bounds that no segment hasa setting angle that is greater than 30 degrees different than thesetting angle of any other segment.
 2. The vortex wall and impellerassembly of claim 1 in which said impeller is divided into modules (32)and the number of segments in said vortex wall is 25 to 50 percentgreater than the number of modules in said impeller.
 3. The vortex walland impeller assembly of claim 1 in which said setting angles varyrandomly among the total number of segments within the bounds that nosegment has a setting angle that is greater than five degrees differentthan the setting angle of any other segment.
 4. The vortex wall andimpeller assembly of claim 1 in which said nose-to-impeller clearancesvary randomly among the segments within the bounds that no segment has aclearance that is less than 0.06 times nor more than 0.08 times saidmaximum swept diameter.